Plasmonic enhancement of absorption in sunscreen applications

ABSTRACT

Zinc oxide compositions as well as techniques for plasmonic enhancement of absorption in sunscreen applications are provided herein. A method includes selecting one or more metal particles to be used in conjunction with one or more zinc oxide particles in a sunscreen composition, wherein said selecting is based on the plasmon resonance frequency associated with each of the metal particles; and embedding the one or more selected metal particles into each of the one or more zinc oxide particles.

FIELD

The present application generally relates to chemical technology, and, more particularly, to sunscreen technologies.

BACKGROUND

Sunscreen creams and other such compositions are commonly used to prevent ultraviolet (UV) radiation (also referred to herein as “light” in this context) from reaching the skin of a human user and causing damage. It is noted that UV light is an electromagnetic radiation with a wavelength range between approximately 280 nanometers (nm) and approximately 400 nanometers (specifically, that is the range of UV radiation that is not absorbed by the ozone).

A common active ingredient of existing sunscreen compositions is zinc oxide (ZnO). ZnO is a semiconductor that has a specific band gap, and particles of ZnO used in existing sunscreen compositions are typically approximately 50-200 nm in size. Additionally, in existing sunscreen compositions, typical ZnO materials are capable of absorbing UV light (that is, blocking the UV light from passing through the sunscreen composition to be absorbed by the skin of the user) within a wavelength range of approximately 290 nm through only approximately 350-380 nm.

Additionally, high sun protection factor (SPF) sunscreen compositions, which can absorb a large majority of the UV light in the range of 290-380 nm, require the addition of a higher density of ZnO particles, which causes the composition to become white and/or opaque due to light scattering from the ZnO particles, and which is an often undesirable property to consumers.

SUMMARY

In one embodiment of the present invention, zinc oxide compositions, methods of fabrications thereof and methods of use thereof are provided. An exemplary method can include selecting one or more metal particles to be used in conjunction with one or more zinc oxide particles in a sunscreen composition, wherein said selecting is based on the plasmon resonance frequency associated with each of the metal particles. The method can also include embedding the one or more selected metal particles into each of the one or more zinc oxide particles.

In another embodiment of the invention, a sunscreen composition can include multiple zinc oxide particles suspended within a medium, and one or more metal particles embedded into each of the multiple zinc oxide particles, wherein each of the metal particles comprises a plasmon resonance frequency that supplements the light absorption capabilities of the multiple zinc oxide particles.

These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a metal particle embedded within a ZnO particle, according to an example embodiment of the invention;

FIG. 2 is a diagram illustrating ZnO particles, each embedded with a metal particle, embedded within a silicon dioxide (SiO₂) particle, according to an example embodiment of the invention;

FIG. 3 is a diagram illustrating multiple metal particles embedded within a ZnO particle; and

FIG. 4 is a flow diagram illustrating techniques, according to an embodiment of the invention.

DETAILED DESCRIPTION

As described herein, an embodiment of the present invention includes ZnO compositions as well as techniques for plasmonic enhancement of absorption in sunscreen applications. As further detailed herein, one or more embodiments of the invention include generating ZnO compositions and methods of use thereof for effectively blocking more and/or all of the complete spectrum of UV light (that is, as noted above, the UV radiation that is not absorbed by the ozone, and which ranges between approximately 280 nm and 400 nm) while also preventing whitening effects caused by the scattering of light in the visible spectrum (that is, radiation between approximately 400 nm and 700 nm). As used herein, “scattering” refers to the deflection of rays of visible light from the rays' original path due to interaction with particle surfaces.

At least one embodiment of the invention includes enhancing light absorption capabilities of ZnO particles by using plasmonic resonances. As detailed herein and illustrated via the example embodiments depicted in FIGS. 1-3, one or more embodiments of the invention can include generating a structure that is designed to utilize the plasmonic enhancement of light intensity near a metal particle surface. In such an embodiment, one or more metal particles are enclosed and/or embedded inside a ZnO particle to generate plasmonic enhancement of absorption in the resulting composition.

FIG. 1 is a diagram illustrating a metal particle 104 embedded within a ZnO particle 102, according to an example embodiment of the invention. In one or more embodiments of the invention, the metallic and/or plasmonic particle 104 can include a silver (Ag) particle or a gold (Au) particle. Also, in at least one embodiment of the invention, the metallic and/or plasmonic particle 104 can be less than 30 nm in diameter (for example, between 10 and 30 nm in diameter). Additionally, the ZnO particle 102 can be approximately 200 nm in diameter (for example, between 100 and 200 nm in diameter) to utilize the plasmonic effect of the metal particle 104 and maximize the plasmonic enhancement absorption of the resultant composition. In accordance with one or more embodiments of the invention, the electric field is only enhanced within approximately 100 nm of the metallic particle 104.

FIG. 2 is a diagram illustrating ZnO particles 102, each embedded with a metal particle 104, embedded within a SiO₂ particle 202, according to an example embodiment of the invention. While the example embodiment depicted in FIG. 2 utilizes a SiO₂ particle 202, it is to be appreciated that one or more embodiments of the invention can utilize any material that has a large band gap (greater than approximately ˜3.2 electron volts (eV), for example) and a refractive index in between that of ZnO and air. Additionally, the SiO₂ particle 202, as depicted in the FIG. 2 example, can be (approximately) between 0.8-2.0 micrometers in diameter.

FIG. 3 is a diagram illustrating multiple metal particles 104 embedded within a ZnO particle 102. In one or more embodiments of the invention, the distance between metal particles 104 can include any distance amount so as to ensure that the metal particles 104 are physically separate from one another. In one example, such as depicted in FIG. 3, the distance between the metal particles 104 can be approximately 100-200 nm. Also, in one or more embodiments of the invention (such as the example embodiment depicted in FIG. 3), the size of each individual ZnO particle 102 can be reduced (for use in a sunscreen composition) to less than 400 nm. By way of example, at least one embodiment of the invention includes reducing the size of each ZnO particle to a size of between approximately 100 and 400 nm.

Further, it is noted that the example ZnO particle depicted in FIG. 3 (embedded with multiple metal particles) can also be utilized as illustrated in FIG. 2; that is, the example ZnO particle depicted in FIG. 3 (embedded with multiple metal particles) can be embedded within a SiO₂ particle 202, in accordance with one or more embodiments of the invention.

FIG. 4 is a flow diagram illustrating techniques, according to an embodiment of the present invention. Step 402 includes selecting one or more metal particles to be used in conjunction with one or more zinc oxide particles in a sunscreen composition, wherein said selecting is based on the plasmon resonance frequency associated with each of the metal particles. Step 404 includes embedding the one or more selected metal particles into each of the one or more zinc oxide particles.

In at least one embodiment of the invention, each of the zinc oxide particles can include a size of less than 400 nanometers in diameter, and each of the one or more metal particles can include a size of less than 30 nanometers. Additionally, the one or more metal particles can include one or more silver particles and/or one or more gold particles. Further, in one or more embodiments of the invention, the one or more metal particles can include multiple metal particles, wherein the multiple metal particles are each physically separated within each of the one or more zinc oxide particles.

The techniques depicted in FIG. 4 can also include selecting one or more suspension particles to be utilized in conjunction with the multiple zinc oxide particles, wherein each of the one or more suspension particles is larger in size than each of the multiple zinc oxide particles, and wherein said selecting is based on the refractive index of each of the one or more suspension particles. One or more embodiments of the invention can also include embedding the multiple zinc oxide particles into the one or more suspension particles. Additionally, in such an embodiment, the one or more suspension particles can include one or more silicon dioxide particles, and each of the one or more suspension particles can include a size of between 0.8 and 2 micrometers. Further, in at least one embodiment of the invention, the refractive index of each of the one or more suspension particles is between that of air and zinc oxide.

Also, an additional embodiment of the invention includes a sunscreen composition that includes multiple zinc oxide particles suspended within a medium, and one or more metal particles embedded into each of the multiple zinc oxide particles, wherein each of the metal particles comprises a plasmon resonance frequency that supplements the light absorption capabilities of the multiple zinc oxide particles. Such a composition can also include one or more suspension particles, wherein each of the one or more suspension particles is larger in size than each of the multiple zinc oxide particles, and wherein each of the multiple zinc oxide particles is embedded into the one or more suspension particles.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of another feature, step, operation, element, component, and/or group thereof.

At least one embodiment of the present invention may provide a beneficial effect such as, for example, generating a structure that is designed to utilize the plasmonic enhancement of light intensity near a metal particle surface.

The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein. 

What is claimed is:
 1. A sunscreen composition comprising: multiple zinc oxide particles suspended within a silicon dioxide particle, wherein each of the zinc oxide particles is between approximately 100 nanometers and approximately 400 nanometers in diameter, and wherein the silicon dioxide particle is between approximately 0.8 micrometers and approximately 2 micrometers in diameter; and nine silver particles embedded into each of the multiple zinc oxide particles, wherein each of the nine silver particles is between approximately 10 nanometers and approximately 30 nanometers in diameter, and wherein the nine silver particles are physically separated within each of the zinc oxide particles by a distance of between approximately 100 nanometers and approximately 200 nanometers between each of the silver particles. 